Cautery protection circuit for a heart pacemaker

• US 4,038,990 A
• Filed: 11/19/1975
• Issued: 08/02/1977
• Est. Priority Date: 11/19/1975
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Thompson, David L.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/633,561
• Time in Patent Office: 622 Days
• Field of Search: 128/2.1 P, 128/419 P, 128/419 PG, 128/419 R, 317/53, 317/D6, 317/33 VR, 333/12, 333/24.1, 333/24.2, 333/76
• US Class Current: 607/9
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371

Abstract

A cautery protection circuit is disclosed for use with a heart pacemaker or generator circuit and comprises circuit elements for preventing those signals induced within the output portion of the heart pacemaker circuit by an electric field established by cautery procedures, from damaging the generator circuit or turning on the generator circuit at an undesired instant in time, whereby, otherwise, a pacemaker pulse signal may be generated to possibly induce fibrillation within the patient'"'"'s heart. The cautery protection circuit of this invention is particularly adapted for use with a bipolar heart pacemaker and in particular includes a torroidal inductor having first and second inductors coupled to each of the output leads and having a high permativity coupling therebetween, whereby when cautery signals are induced in the output leads associated with the patient'"'"'s heart, the coupled inductors operate in a "common mode" configuration to, in effect, "multiply" or increase the inductance presented thereby to the induced signals, thus significantly limiting the current passed therethrough. The coupled inductors of the torroidal inductor also operate in a "differential mode" wherein a pacemaker pulse as generated by the pacemaker generator circuit is applied thereto in a manner such that the fields induced in the coupling between the first and second inductors is opposing, whereby the inductors provide a low or substantially 0 inductance to the pacemaker pulse and thus, impose substantially no shaping upon the output pulses.

Claims

1. A bipolar heart pacemaker circuit comprising:

a. a pulse generator for generating a control signal at a desired rate according to that with which it is desired to stimulate a patient'"'"'s heart;

b. output switch means responsive to the control signal for providing a heart stimulating output pulse to be applied by first and second leads to the patient'"'"'s heart; and

c. a torroidal inductor including first and second inductors, each connected in-series with a corresponding one of said first and second leads and coupled together by a high coefficient of coupling to operate in a first mode in the presence of a cautery-inducted field, wherein the signals applied to said first and second inductors by the cautery-induced field induce fields in the same direction through said coupling and the inductances offered to the cautery-induced signals are correspondingly increased, and in a second, differential mode in response to the application of a pacemaker pulse signal wherein opposing fields are established through said coupling between said first and second inductors so that the inductances offered by said first and second inductors are significantly reduced, said torroidal inductor comprising a torroidal core having permeability in the order of 120, a bandwidth of not less than 10MHz and a resonant frequency of not less than 5MHz, whereby the impedance presented to said pulse generator is reduced and distortion applied to the heart stimulating output pulse is reduced.